The invention relates to a device for the rotary and simultaneous electroinductive hardening of the bearing surfaces of crank pins of a crankshaft disposed immediately one beside the other and offset in relation to one another in the axial direction, having inductors which each engage around the crank pins by a maximum of 180.degree. and which each have two inductor branches arranged in parallel and following the curvature of the bearing surfaces, of which one branch is associated with the overlapping zone of the crank pins, the other branch being associated with the particular other edge zone of the crank pin associated therewith, the inductor branches of each inductor having in the axial direction a distance increased in relation to half the total width of the crank pins.
In crankshafts having crank pins disposed offset immediately one beside the other, also known by the term "split pin crankshafts", there is the basic problem that with the individual hardening of each bearing surface the previously hardened immediately adjacent bearing surface is annealed by the heating of the following hardened bearing surface. For this reason, for example, German Patent Specification DE 42 36 921 C1 suggests that the hardening of the immediately adjacent bearing surface of a split pin crankshaft should be performed simultaneously. Associated with each crank pin is an inductor, the inductors being disposed substantially diametrically opposite. This diametrically opposite, offset arrangement has the advantage that the space available on both sides of the crankshaft can be used for the arrangement of supply and control devices for the operation of the inductors. Another advantage of the diametrically opposite arrangement of the inductors is that it enables the width of the individual inductors--i.e., the distance between the inductor branches--to be so selected that the sum of the width of two inductors is greater than the total width of two bearing surfaces to be hardened. The radially opposite arrangement ensures that even though they overlap in the axial direction because of the increased width, the inductors do not collide when the crankshaft rotates.
Another problem in the electroinductive hardening of immediately adjacent bearing surfaces of a crankshaft is that as a rule cheeks are formed which are constructed laterally of the crank pins disposed directly one beside the other and which cheeks have a larger volume of material than the crank pins disposed therebetween.
When the bearing surfaces become heated, the accumulation of material in the zone of the cheeks results in a reduction in heat in the zone of the bearing surface edge zones associated with the cheeks. To obviate this problem German Patent Application 195 30 430 suggests that the inductor branch associated with the cheek side edge zone of the bearing surface to be hardened should be constructed longer than the inductor branch disposed in the overlapping area of the crank pins. This achieves a uniform temperature distribution in the electroinductive heating of bearing surfaces.
The afore-explained devices have proved themselves in practical trials, but it has been found that it is technically very expensive so to guide the diametrically opposite inductors and keep them bearing against the bearing surface to be hardened that on the one hand any damage to the bearing surface is impossible, while on the other hand the close electroinductive coupling of the inductor and the bearing surface is ensured necessary for the effective heating of the bearing surface.
Neither could the cost of guiding the inductors be reduced by the rearrangement of the electric supply elements, as also known from practice, to enable the inductor casings to be jointly brought in from one direction from above. Even with inductors thus supplied from above, each of the inductor branches operative during heat generation had to be disposed substantially diametrically opposite, to prevent them from colliding when the crankshaft rotated.
It is an object of the invention to provide a device of the kind specified in which the technical cost of guiding the inductors is reduced, while at the same time an optimum heating and hardening result is ensured.